Investigating Digestive Enzymes

As, like the gut, it only lets small molecules through and not big molecules. It's also a lot cheaper, easier and less yukky than using an animal's gut.

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How is visking tubing not exactly the same as the gut? What does this mean?

Your gut is a lot longer and has a massive surface area - so the speed of digestion and absorption will be slightly different. So visking tubing is not an exact model, but it's good enough to see how digestive enzymes work.

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What can you use to test starch and sugar? (EXPERIMENT -1)

Iodine to test starch and Benedict's to test for sugar.

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What do you do firstly? (2)

1) Add the same volume of starch suspension and 0.25% amylase solution to the visking tubing, then rinse the outside of the tubing under a tap.

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What do you do secondly? (3)

2) Put the visking tubing into a boiling tube with distilled water in it.

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What do you do thirdly? (4)

3) Straight away test a drop of water from around the visking tubing with iodine solution, and take 5 drops to test with Benedict's reagent. Record the colour each time.

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Describe how to use Benedict's reagent and the colour change (5)

Add 5 drops of into a test tube. Add a drop Benedict's reagent and put the test tube into a beaker of boiling water. Record the colour after 2-3 mins. blue-green-yellow-orange-black red. Will change colour if sugar is present.More sugar=more col chan

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What do you do fourthly? (6)

4)Leave the boiling tube for 15 minutes.

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What do you do fifthly? (7)

5) Then test the water again with iodine solution and Benedict's reagent. Record the colour each time.

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What do you do lastly? (8)

6) Repeat the experiment using other concentrations of the amylase solution, (e.g, 0.5%,1.0%,1.5%,2.0%)

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What does the organgey-brown colour of iodine solution show?

That no starch is present in the water. This is because the starch molecules are too big to pass through the visking tubing into the water.

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What does the colour change of Benedict's reagent from blue show? Why?

That sugar is present in the water. This is because starch has been broken down by amylase to sugar in the visking tubing, and the sugar molecules are small enough to pass through the membrane into the water.

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Describe the trend with concentration of amylase and colour change. What does this mean? (1A)

The higher the concentration of amylase, the further the Benedict's reagent has changed colour. This means lots more starch has been broken down to sugar.

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Why has lots of more starch been broken down to sugar? (2A)

As at a higher concentration of amylase, there are more active sites available to break down the starch into sugar, so the starch is broken down at a faster rate.

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But what happens above a certain amylase concentration? (3A)

The reaction won't get any faster because there are already enough active sites to deal with all the starch. This can be shown on a graph.

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Card 2

Front

How is visking tubing not exactly the same as the gut? What does this mean?

Back

Your gut is a lot longer and has a massive surface area - so the speed of digestion and absorption will be slightly different. So visking tubing is not an exact model, but it's good enough to see how digestive enzymes work.